JP2017077597A - drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute up to finish processing from rough processing, while securing high accuracy processing by high sharpness and the tool service life.SOLUTION: A drill 1 is formed by opposing a pair of chip discharge grooves 6 of extending to the rear end side from a tip surface 2a of a drill body 2 to a tip side outer peripheral surface, and a main cutting edge 7 is formed in a crossing part between a surface of turning to the rotational direction of the chip discharge grooves 6 and the tip surface 2a. A thinning cutting edge 14 is formed toward the central axis O side of becoming the rotational center of the drill body 2 from the main cutting edge 7. A small-width chisel core thickness 15 is formed by sandwiching the central axis O between the opposed thinning cutting edges 14. The chisel core thickness 15 in the tip surface 2a of the drill body 2 has a thickness of 0.8-3% of a maximum outer diameter D. The thinning cutting edge 14 has a projection part 14a of projecting forward in the rotational direction to the center line L of a virtual line of connecting the central axis O and an outer peripheral edge 11 formed on an extension line of the main cutting edge 7.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a drill that is used for drilling holes in, for example, precision machine parts, precision machined parts, and the like, and can drill holes with high accuracy even if the work surface of the work material is an inclined surface.

A drill that is attached to a milling machine, a machining center, a lathe, or the like and used for drilling has a sharp tip in a fan shape or a convex shape so that the cutting edge at the tip of the tool is linearly bite into the work material. On the other hand, recent drills are known in which the cutting edge of the cutting edge portion is made flat so that holes can be drilled in the slope of the work material.
For example, the drill described in Patent Document 1 is a flat drill in which a pair of cutting blades at the tip has a tip angle of 180 degrees, and a flank formed on the tip and a thinning surface formed on the chip discharge groove. The intersecting ridgeline is the cutting edge.

In addition, the drill described in Patent Document 2 has a fan-shaped cutting edge, and the first is at the intersection of the rake face having a positive rake angle formed in two opposing chip discharge grooves and the tip face. A cutting edge is formed, and a second cutting edge is formed at the intersection of the thinning surface formed at the thinning portion including the recess including the chip discharge groove and the tip surface. The second cutting edge is connected to the first cutting edge and intersects the chisel edge.
In this drill, the ratio of the tool diameter to the distance between two opposing thinnings is set to 15% or more and 35% or less, and if it is smaller than this range, the strength of the tip is insufficient and breakage occurs when biting. Breaking is likely to occur, and conversely, if it is large, the drill sways during processing, and the processing hole expands to reduce the processing accuracy.

JP 2002-66822 A International Publication No. 2012/070640

However, since the drill described in the above-mentioned Patent Document 1 has a large core thickness, if a hole is drilled on an inclined surface or the like, the cutting edge at the tip portion escapes and is distorted, so that the hole diameter is widened. In addition, since the machined surface is rough, there are defects in machining accuracy such as burrs occurring at the entrance and exit of the machined hole.
Further, in the drill described in Patent Document 2, since the distance between two thinnings is set to 15% to 35%, the rigidity of the drill can be secured, but the thickness between the thinnings is larger than the tool diameter. Therefore, as in Patent Document 1, the whirling occurs, and it is difficult to perform high-precision processing with high sharpness.

  In addition, the above-described conventional drills use 3 to 4 types of tools such as center drill (grinding), drill (preparation), drill, and reamer (finishing) for high-precision machining. Therefore, there is a disadvantage that the number of processes is increased due to the complicated tool change.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a drill capable of performing from roughing to finishing while ensuring high-precision processing and tool life due to high sharpness. To do.

In the drill according to the present invention, a chip discharge groove extending from the front end surface of the drill body to the rear end side is formed on the outer peripheral surface of the front end side, and the main cutting edge is formed at the intersection of the surface facing the rotation direction of the chip discharge groove and the front end surface. And a thinning blade is formed from the main cutting edge toward the central axis that is the rotation center of the drill body, and a core thickness is formed by sandwiching the central axis between opposing thinning cutting edges. The core thickness is 0.8 to 3% of the maximum outer diameter D, and the thinning blade is an extension of the central axis and the main cutting edge. It is characterized by having a shape having a convex portion protruding forward in the rotational direction with respect to a virtual line connecting the outer peripheral blade formed above.
According to the present invention, since the core thickness is set to be small between 0.8% and 3% of the maximum outer diameter D of the drill body, the work material can bite well and machining accuracy can be prevented by preventing runout during drilling. In addition, it is possible to increase the rigidity of the core thickness by increasing the rigidity by forming a convex portion on the thinning cutting edge. Therefore, even when the work surface of the work material is an inclined surface or the like, the cutting edge portion is well bitten and high drilling accuracy and tool life can be obtained.
The convex part of the thinning cutting edge protrudes in the rotation direction within the range of 2 to 5% of the maximum outer diameter D of the drill, so that the rigidity of the thinning cutting edge and the core thickness can be increased and the thickness of the core thickness can be increased. Even if it is made smaller, chipping is not generated and the tool life can be improved.

Moreover, it is preferable that the thinning rake face is formed in the surface which faces the rotation direction front of a chip | tip discharge groove | channel, and the rake angle of a thinning rake face is a positive angle of 5 degrees-20 degrees.
Even if the convex portion is formed on the thinning cutting edge, since the rake angle of the thinning rake face is set to a positive angle of 5 ° to 20 °, high sharpness and hole machining accuracy can be obtained.

In addition, a thinning portion provided with a concave shape of a thinning depth that is provided in the rotation direction of the main cutting edge and extends from the outer peripheral surface to a region exceeding the central axis to form a core thickness, and the concave shape of the thinning portion The cross section may be formed in a substantially polygonal shape or a substantially arc shape.
Since the thinning portion including the chip discharge groove has a thinning depth that extends to a region exceeding the central axis to form a core thickness, it is possible to ensure the chip discharge performance and the rigidity of the blade edge portion.
In addition, when the rake face of the thinning cutting edge is viewed in front, the thinning through angle α of the thinning surface formed in the thinning part is set in the range of 25 ° to 45 °, so the core thickness and strength reduction of the thinning surface are suppressed. However, it is possible to improve the discharge of chips generated by the thinning cutting blade.

Also, on the tip surface of the drill body, a first margin that protrudes toward the rear side in the rotational direction on the outer peripheral surface provided with the outer peripheral blade, and a second margin that protrudes from the rear side in the rotational direction of the first margin. And a margin.
When the outer diameter of the drill body is more than 2.5 mm to 6 mm, the first margin and the second margin are formed by drilling by forming the first margin and the second margin at an interval on the outer peripheral surface of the cutting edge. The machining is guided by abutting against the machining surface of the hole, and the cutting process is guided, and the drill hole is suppressed to obtain the high machining hole accuracy equivalent to the finishing process by the reamer.
Further, by setting the rake angle of the rake face of the second margin 25 to a negative angle of 20 ° to 70 °, the machining hole of the second margin is prevented from biting into the machining surface and the roughness of the machining surface is reduced. It can be prevented from getting worse.

  According to the drill of the present invention, by reducing the core thickness and causing the thinning cutting edge to protrude in the tool rotation direction, the whirling during the cutting process is suppressed to ensure high processing accuracy and the rigidity of the core thickness is increased. High and long life can be obtained.

It is a side view of the drill by embodiment of this invention. It is an enlarged side view of the blade edge | tip part of the front-end | tip of the drill shown in FIG. FIG. 3 is a front end view of a cutting edge portion of the drill shown in FIG. 2. It is an enlarged view of the chisel core thick part of the drill shown in FIG. It is the side view which looked at the drill shown in FIG. 2 from 90 degrees different. It is a front end view which shows the blade edge | tip part of the drill by a modification.

As shown in FIG. 1, a drill 1 according to the present embodiment includes a drill body 2 made of a hard material such as tool steel or cemented carbide, which is rotatable about a central axis O and formed in a substantially cylindrical shape. ing. The portion on the rear end side (left side in FIG. 1) of the drill body 2 is a shank portion 3 that is gripped by the rotating shaft of the machine tool, while the tip end portion is a blade edge portion 4 that processes the work material. Yes.
The drill 1 is suitable for drilling holes in precision machine parts, precision machined parts, and the like, and uses, for example, non-ferrous metals, general steel materials, heat-resistant alloys, and the like as work materials. In the drill 1 according to this embodiment, the cutting edge portion 4 side is referred to as a front end side, and the shank portion 3 side is referred to as a rear end side.

On the outer peripheral side surface of the cutting edge portion 4 of the drill 1, a pair twisted toward the rear side in the drill rotation direction T at a constant twist angle from the front end side (right side in FIGS. 1 and 2) toward the rear end side in the central axis O direction. The chip discharge grooves 6 are formed in a spiral shape in a symmetrical arrangement with respect to the central axis O. Further, a main cutting edge 7 is formed to face each other at the intersection between the chip discharge groove 6 and the tip end surface 2 a of the drill body 2.
2 and 3, the tip region of the wall surface of the main cutting edge 7 facing the drill rotation direction T of the chip discharge groove 6 is a rake face 8. As shown in FIG. 3, a flank 10 is provided on the distal end surface 2 a of the drill body 2 behind the main cutting edge 7 in the rotational direction. The rake angle and clearance angle of the thinning cutting edge 14 can be set to appropriate positive angles, and the rake angle can be set to about 5 ° to 20 °, for example, but may be outside this range.

  In the front end surface 2a of the blade edge portion 4 shown in FIG. 3, the pair of main cutting blades 7 have two blades disposed at positions facing each other by 180 degrees in the front end surface 2a and in the direction of the central axis O perpendicular thereto. It is composed. Therefore, the drill 1 constitutes a flat drill. The drill 1 according to the present embodiment is suitably used, for example, for machining a blind hole with a sealed tip, a seat for a countersink hole, a head hole for a cap bolt, a shallow screw hole, or a hole for a slope.

Further, a flank 10 is disposed on the distal end surface 2 a of the drill body 2 in a rotationally symmetrical manner about the central axis O at the rear of the main cutting edge 7 in the rotational direction. The flank 10 is provided with a second flank 10a having a positive flank on the rear side in the rotational direction of the main cutting edge 7, and a third flank 10b with a larger flank is formed behind the flank. An outer peripheral edge 11 is provided along the chip discharge groove 6 at the outer peripheral end of the pair of main cutting edges 7.
Further, a thinning groove including the chip discharge groove 6 is formed by cutting the outer peripheral surface into a concave shape between one main cutting edge 7 and the flank 10 of the other main cutting edge 7 formed in the rotation direction. It is formed as part 12.

On the distal end surface 2a of the drill body 2 shown in FIGS. 3 and 4, a thinning cutting edge 14 is formed on the center axis O side of the pair of main cutting edges 7 respectively. These thinning cutting edges 14 form a convex portion 14a that protrudes forward in the rotational direction of the main cutting edge 7 from the connecting portion with the main cutting edge 7, and the other end 14b extends beyond the vicinity of the central axis O on the opposite side. The thinning cutting blades 14 extend to a position overlapping with the other end portion 14b of the thinning cutting edge 14 in parallel. In the present embodiment, the cutting edge composed of the main cutting edge 7 and the thinning cutting edge 14 is formed 180 degrees rotationally symmetric about the central axis O.
As shown in the enlarged view of FIG. 4, the other end portions 14b of the thinning cutting blades 14 overlap with each other at a predetermined minute interval in the regions on both sides of the central axis O, and the thickness between the other end portions 14b. The part has a chisel core thickness of 15. The intersecting ridgeline between the second flank surfaces 10a that pass through the central axis O and obliquely intersect the chisel core thickness 15 is a chisel blade 17. The chisel blade 17 is a cutting blade including the central axis O having the smallest peripheral speed of the drill body 2, and can cut the work material at a low speed.

  Here, the distance between the pair of outer peripheral blades 11 arranged to face each other at 180 degrees on the tip surface 2 a of the blade edge portion 4 shown in FIG. 3 is defined as the maximum outer diameter D of the blade edge portion 4. The outer diameter D of the drill 1 is set to φ6 mm or less, for example, in the range of φ0.5 mm to φ6 mm. The drill 1 according to the embodiment is set to about φ3 mm, for example.

  And the convex part 14a of the thinning cutting blade 14 protrudes in the polygonal shape or the circular arc shape or the convex curve shape with respect to the center line L which passes the central axis O and is the virtual line which connects the outer periphery blades 11 with each other. I am letting. The maximum protrusion amount P with respect to the center line L of the convex portion 14a was set in the range of 2% to 5% of the outer diameter D. The convex portion 14a can increase the rigidity of the thinning cutting edge 14 and the chisel core thickness 15, and even if the thickness t of the chisel core thickness 15 is reduced, no chipping occurs during cutting, and the life of the drill 1 can be improved. On the other hand, if the protrusion amount P is less than 2%, there is no effect in improving the rigidity of the thinning cutting edge 14 and suppressing the chip thickness of the chisel core thickness 15. If it exceeds 5%, the chip discharge groove 6 is narrowed and generated by the thinning cutting edge 14. Reduces the discharge of chips.

Moreover, the thickness t of the chisel core thickness 15 is set in the range of 0.8% to 3.0% of the outer diameter D of the blade edge portion 4. Within this range, the cutting resistance in the vicinity of the central axis O at the time of rotary machining can be reduced to suppress the whirling so that highly accurate drilling can be performed, and the chisel core thickness 15 is related to the convex portion 14a of the thinning cutting edge 14. Deficiency can be suppressed. On the other hand, if it is less than 0.8%, the chisel core thickness 15 tends to be easily lost during cutting, and if it exceeds 3.0%, it tends to cause blurring during cutting and the hole machining accuracy cannot be improved.
And by forming the convex part 14a in the thinning cutting edge 14, the rake angle θ of the rake face 16 of the thinning cutting edge 14 formed in the chip discharge groove 6 is 5 ° to 20 ° as shown in FIG. Can be set in the range of °. Thereby, the rake angle equivalent to that of the main cutting edge 7 can be brought close to, and the sharpness of the cutting edge portion 4 can be enhanced. If the rake angle θ of the thinning cutting edge 14 is smaller than 5 °, the cutting edge strength is high but the sharpness is lowered, and if it exceeds 20 °, the cutting edge is increased but the cutting edge is easily lost.

In order to smoothly discharge the chips generated by the thinning cutting edge 14 during drilling, the recessed thinning portion 12 including the chip discharge groove 6 includes the chip discharge groove 6 from the outer peripheral surface of the cutting edge portion 4 and the central axis. A recess is formed so as to extend in the O direction and exceed the central axis O, and a thinning depth is formed so that a chisel core thickness 15 having a predetermined width t is formed by the tip recesses of the pair of thinning portions 12. In the example shown in FIGS. 3 and 4, the shape of the concave portion at the tip of the thinning portion 12 is formed in a polygonal shape, for example.
Moreover, as shown in FIG. 2, the rake face 16 of the thinning cutting edge 14 is viewed from the front, and an angle with respect to the central axis O of the thinning face 20 for discharging chips generated by the thinning cutting edge 14 in the thinning portion 12. A certain thinning through angle α was set in a range of 25 ° to 45 °. Thereby, the chip | tip discharge property by the thinning cutting blade 14 can be improved, suppressing the intensity | strength fall of the thinning surface 20. FIG. Further, the chips generated by the thinning cutting edge 14 can be discharged to the base end side.

Further, if the thinning depth of the thinning portion 12 is large, the width t of the chisel core thickness 15 becomes small and the rigidity is lowered and the chipping is likely to be lost. By setting the angle α in the range of 25 ° to 45 ° described above, the rigidity can be supplemented, and chip dischargeability and rigidity can be ensured. That is, if the thinning through angle α is in the range of 25 ° to 45 °, the strength of the thinning surface 20 is relatively small, but the necessary strength can be ensured and the chip discharge performance by the thinning cutting edge 14 is good.
On the other hand, when the thinning through angle α is smaller than 25 °, the chip discharging property is further improved, but there is a disadvantage that the strength of the thinning surface 20 is lowered. When the thinning through angle α is greater than 45 °, the strength of the thinning surface 20 is increased, but the chip discharging performance by the thinning cutting edge 14 is lowered.

  Further, in the distal end surface 2a of the cutting edge portion 4 shown in FIG. 3, a first margin 22 is formed on the outer peripheral surface on the rear side in the rotation direction of the outer peripheral blade 11 along the processing surface (inner wall surface) of the hole by the drill 1. Yes. An outer peripheral surface 24 having a reduced diameter due to a step 23 is formed on the rear side in the rotation direction of the first margin 22, and a second margin 25 is formed on the rear side thereof so as to protrude along the processing surface of the hole. A second flank 10a of the main cutting edge 7 is formed on the front end surface 2a intersecting the first margin 22, and a third flank 10b is formed on the rear side of the tip margin 2a through the outer margin 24 to the second margin 25. ing.

The first margin 22 has a land portion 22a formed of a small cylindrical surface centered on the central axis O in a plan view of the drill 1 shown in FIG. 3 and a positive clearance angle formed behind the first margin 22. A flank 22b is formed. The land portion 22a has a width in the range of 0.3% to 3% of the outer diameter D, and no clearance angle is formed. The land portion 22a abuts the hole machining surface to guide the hole machining, but the flank 22b does not abut the machining surface.
Therefore, the first margin 22 can suppress the biting of the processed hole on the processed surface, compressive stress, and chatter vibration during the hole processing, and the land portion 22a can be in contact with the processed surface and leveled.

A second margin 25 is formed so as to protrude through the outer peripheral surface 24 behind the flank 22 b of the first margin 22 in the rotation direction. The first margin 22 and the second margin 25 are spaced at an angle γ of 70 ° to 90 ° in the circumferential direction. The second margin 25 has a substantially cylindrical surface shape with a clearance angle of 0 ° and is in contact with the processed surface of the hole.
The second margin 25 is preferably set to a width in the range of 2% to 8% of the outer diameter D of the drill 1. Within this range, the second margin 25 is installed behind the first margin 22 in the drill 1 to suppress the whirling (chatter vibration) of the drill 1 during drilling and guide the linear descent of the drill 1. can do.
If the width of the second margin 25 is less than 2% of the outer diameter D, the guide property of the drill 1 is weak, and there is a drawback that the hole diameter is widened without suppressing the swinging of the tool. The contact area of the machined hole of the cutting material increases, the frictional heat increases by increasing the cutting resistance, and the hole diameter is increased by welding the work material and chips to the outer surface of the second margin 25. , The disadvantage is that the processed surface is significantly roughened.

  Further, the second margin 25 needs to be set at a rake angle so as not to cut the machined surface for the guide action of the drill 1. For example, when the rake angle of the rake face 25a facing the rotation direction of the second margin 25 is in the range of less than 20 ° from a positive angle to a negative angle, the machining surface is likely to bite and the machining hole is enlarged or the machining surface is There is a disadvantage that it is roughened. For this reason, it is preferable to set the rake angle of the rake face 25a to a negative angle in the range of 20 ° to 70 ° so as not to cut the machined surface.

Further, the second margin 25 is such that when the outer diameter D of the drill 1 is 2.5 mm or less, the tool diameter is thin, so that the tool rigidity is small, the tool is bent, and the hole diameter of the machining hole is increased. Is easy to break. For this reason, it is necessary to reduce the rotation speed of the cutting conditions to suppress the tool swing and further to set the feed speed per one revolution, so that the machining efficiency is lowered.
As a means for solving these negative phenomena, it is preferable that only the first margin 22 is formed on the outer peripheral surface of the cutting edge portion 4 and the second margin 25 is not installed. In addition, since the tool diameter of the drill 1 is as small as 2.5 mm or less, it is technically difficult to form the second margin 25, and even if the second margin 25 is formed, cutting resistance is generated and breakage occurs. Cause. In this case, by forming only the first margin 22 on the outer peripheral surface of the cutting edge portion 4, even a small diameter tool can be drilled without lowering the machining efficiency.

  When the outer diameter D of the drill 1 is more than φ2.5 mm, it is preferable to install the second margin 25 in the first margin 22 under the above-described conditions. In this case, in the drilling of the work material by the drill 1, the first margin 22 and the second margin 25 are in contact with the processing surface and are guided, so that a hole diameter accuracy substantially equal to that of the reamer processing can be obtained. Therefore, the hole diameter accuracy can realize H5 to H6 with fit tolerance, for example.

In addition, you may coat the hard-coat of multilayered structures, such as TiAlN, on the blade edge | tip part 4 of the drill 1 by this embodiment. In this case, it is preferable that the drill 1 is coated from the tip of the cutting edge portion 4 to a length equal to or less than the tool diameter D, and the subsequent portion of the chip discharge groove 6 is not coated.
As the characteristics of the drill 1, since the tool tip portion is mainly the main cutting edge 7, the hardness, abrasion resistance, and heat resistance of the coating film effective for only that portion are required. When the coating is applied to the portion of the discharge groove 6, the irregularities (droplets) on the coating surface become a resistance when discharging the chips, resulting in a disadvantage that it is difficult to discharge the chips. Therefore, as described above, coating from the tip of the drill 1 to a length equal to or smaller than the outer diameter D of the drill 1 allows the chip discharge groove 6 after that to have no droplet irregularities, resulting in good chip slippage. Chips are discharged smoothly from 6.
Note that the drill 1 according to the present embodiment can perform non-step drilling up to about twice the maximum outer diameter D of the cutting edge portion 4 according to the length of the chip discharge groove 6.

As described above, according to the drill 1 according to the present embodiment, the thinning edge 14 formed by connecting the leading edge 7 of the cutting edge 4 to the main cutting edge 7 and the central axis O side is opposed by 180 degrees. In addition, since the main cutting edge 7 is formed in a flat shape and the chisel core thickness 15 is formed in a small width t of 0.8% to 3% of the outer diameter D, the processing surface of the work material is a slope. In addition, the main cutting edge 7 has good biting and high hole accuracy and machined surface roughness can be obtained.
Further, the thinning is performed by projecting the convex portion 14a of the thinning cutting edge 14 in the rotational direction with respect to the center line L passing through the outer peripheral edge 11 and the central axis O in the range of 2% to 5% of the outer diameter D of the drill 1. The rigidity of the cutting blade 14 can be increased. Moreover, even if the chisel core thickness 15 is set to be 0.8% to 3% of the outer diameter D, the rigidity can be increased by the convex portion 14a of the thinning cutting edge 14, so that the chipping hardly occurs.
Moreover, since the rake angle of the rake face 16 can be set to a positive angle in the range of 5 ° to 20 ° by forming the convex portion 14a on the thinning cutting blade 14 to increase the rigidity, the sharpness of the thinning cutting blade 14 can be set. Can be increased.

  Further, as the pair of thinning portions 12, recesses are formed so as to bite each other up to a region exceeding the central axis O including the chip discharge groove 6, thereby forming a chisel core thickness 15 having a small width t. When the rake face 16 is viewed in front, the thinning through angle α of the thinning surface 20 is set in the range of 25 ° to 45 ° in the thinning portion 12, so that the thinning is performed while suppressing the strength reduction of the chisel core thickness 15 and the thinning surface 20. The discharge property of the chips generated by the cutting blade 14 can be improved.

Further, when the outer diameter D of the drill 1 is more than 2.5 mm, the first margin 22 and the second margin 25 are formed on the outer peripheral surface of the outer peripheral blade 11 of the cutting edge portion 4 so as to be 70 ° to 90 ° apart from each other. The land portion 22a and the second margin 25 are in contact with the machining surface of the drilled hole by the drill 1 to guide the machining, thereby suppressing the swing of the drill 1 and equivalent to the finishing by the reamer. High hole accuracy can be obtained.
Furthermore, by setting the rake angle of the rake face 25a of the second margin 25 to a negative angle of 20 ° to 70 °, the second margin 25 is prevented from biting into the machining surface during drilling. It is possible to prevent the roughness from being deteriorated.

  Further, when the outer diameter D of the drill 1 is 2.5 mm or less, the second margin 25 is not provided, and the first margin 22 is used to guide the small-diameter hole processing, so that the breakage due to the cutting resistance of the second margin 25 can be prevented. Can be prevented. Moreover, even the small-diameter drill 1 can perform hole drilling without reducing the machining efficiency.

As mentioned above, although the drill 1 by embodiment of this invention was demonstrated, this invention is not limited to such embodiment, A various different form and aspect can be employ | adopted within the range which does not deviate from the meaning of this invention. Needless to say. These are all included in the scope of the present invention.
Next, modified examples of the present invention will be described, and the same or similar parts or parts as those of the above-described embodiment will be described using the same reference numerals.

FIG. 6 shows a drill 1A according to a modified example of the present embodiment. The drill 1A according to the modified example is different from the drill 1 according to the embodiment in the rotational direction of the pair of main cutting edges 7 and the thinning cutting edge 14. A pair of recessed thinning portions 30 formed in the front are formed at positions facing each other by 180 degrees. The pair of thinning portions 30 are formed from the opposed positions of the outer peripheral surface of the blade edge portion 4 toward the central axis O and bite each other up to a region beyond the central axis O, similarly to the thinning portion 12 according to the above-described embodiment. Thus, the thinning depth is formed to form the chisel core thickness 15 having a predetermined width t. In addition, in this modification, the thinning portion 30 is formed such that the tip portion is curved in a substantially arc shape.
Thus, the chips generated by the thinning cutting edge 14 can be discharged from the rake face 16 through the thinning portion 30 to the rear end side. Moreover, when the rake face 16 of the thinning cutting edge 14 is viewed from the front, the thinning through angle α of the thinning face 20 for discharging chips generated by the thinning cutting edge 14 in the thinning portion 12 is in the range of 25 ° to 45 °. Therefore, it is possible to improve the chip discharging performance by the thinning cutting edge 14 while suppressing the strength reduction of the thinning surface 20.

Moreover, in the drill 1 by embodiment mentioned above, although the main cutting edge 7 and the thinning cutting edge 14 which were formed in the front end surface 2a of the blade edge | tip part 4 were formed in flat shape, the drill by this invention needs to be necessarily formed in flat shape. Rather, the tip angle may be a tapered convex shape or a sector shape.
Further, in the above-described embodiment and modification, the drill 1 is formed with a two-blade provided with a pair of main cutting blades 7 and a thinning cutting blade 14, but may be configured with a three-blade or a four-blade. . Further, in the above-described embodiment, the main cutting edge 7 and the thinning cutting edge 14 of the drill 1 are set as equal blades, but they may be unequal blades.

DESCRIPTION OF SYMBOLS 1 Drill 2 Drill main body 2a Front end surface 4 Cutting edge part 6 Chip discharge groove 7 Main cutting edge 8, 16 Rake face 10 Relief face 11 Outer peripheral edge 12, 30 Thinning part 14 Thinning cutting edge 14a Convex part 15 Chisel core thickness 20 Thinning surface 22 First margin 22a Land 25 Second margin 25a Rake face

In the drill according to the present invention, a chip discharge groove extending from the front end surface of the drill body to the rear end side is formed on the outer peripheral surface of the front end side, and the main cutting edge is formed at the intersection of the surface facing the rotation direction of the chip discharge groove and the front end surface. And a thinning blade is formed from the main cutting edge toward the central axis that is the rotation center of the drill body, and a core thickness is formed by sandwiching the central axis between opposing thinning cutting edges. The core thickness has a thickness of 0.8 to 3% of the maximum outer diameter D, and the main cutting edge is formed with a regular rake angle. , thinning cutting edge, which has a protrusion protruding forward in the rotational direction relative to the imaginary line connecting the outer peripheral edge formed at the central axis and the extension of the major cutting edge, convex portions are the axial thicknesses and main selector Projects forward in the rotational direction from the blade, and the thinning blade rotates the chip discharge groove. The rake angle on the surface facing the direction forward thinning rake face that is a positive angle is formed, characterized in.
According to the present invention, since the core thickness is set to be small between 0.8% and 3% of the maximum outer diameter D of the drill body, the work material can bite well and machining accuracy can be prevented by preventing runout during drilling. In addition, it is possible to increase the rigidity of the core thickness by increasing the rigidity by forming a convex portion on the thinning cutting edge. Therefore, even when the work surface of the work material is an inclined surface or the like, the cutting edge portion is well bitten and high drilling accuracy and tool life can be obtained.
The convex part of the thinning cutting edge protrudes in the rotation direction within the range of 2 to 5% of the maximum outer diameter D of the drill, so that the rigidity of the thinning cutting edge and the core thickness can be increased and the thickness of the core thickness can be increased. Even if it is made smaller, chipping is not generated and the tool life can be improved.

Moreover, it is preferable that the rake angle of the thinning rake face of the thinning cutting edge is 5 ° to 20 ° .
Even if the convex portion is formed on the thinning cutting edge, since the rake angle of the thinning rake face is set to a positive angle of 5 ° to 20 °, high sharpness and hole machining accuracy can be obtained.

Claims (4)

A chip discharge groove extending from the front end surface of the drill body to the rear end side is formed on the outer peripheral surface of the front end, and a main cutting edge is formed at the intersection of the surface facing the rotation direction of the chip discharge groove and the front end surface, A drill in which a thinning cutting edge is formed from the main cutting edge toward the center axis side of the drill body,
A core thickness is formed across the central axis between the opposing thinning cutting edges,
The maximum outer diameter on the tip side of the drill body is D, and the core thickness is 0.8 to 3% of the maximum outer diameter D,
The thinning cutting blade has a shape having a convex portion protruding forward in the rotation direction with respect to a virtual line connecting the central axis and an outer peripheral blade formed on an extension of the main cutting blade. .   The thinning rake face is formed on a surface of the thinning rake face that faces forward in the rotational direction of the chip discharge groove, and the rake angle of the thinning rake face is a positive angle of 5 ° to 20 °. Drill.   A thinning portion that is provided in the rotational direction of the main cutting edge and extends from the distal end side outer peripheral surface to a region exceeding the central axis to form the concave portion, and has a concave shape at the distal end of the thinning portion The drill according to claim 1, wherein the cross section is formed in a substantially polygonal shape or a substantially arc shape.   A first margin that protrudes toward the rear side in the rotational direction on the outer peripheral surface provided with the outer peripheral blade on the front end surface of the drill body, and a first margin that protrudes from the rear side in the rotational direction of the first margin. The drill according to any one of claims 1 to 3, comprising two margins.

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